1. Field of the Invention
This invention is related to thermosetting powder coating compositions and particularly to epoxy-based compositions that are useful to prime substrates in preparation for the application of a topcoat.
2. Description of the Prior Art
Primers are widely used in preparation for the topcoating of metal or steel substrates to form a smooth surface over which the topcoat is applied. Epoxy-based primer compositions have been used since it is generally known that epoxides give better corrosion resistance and chip resistance than, for example, most alkyd resin primers. Epoxy-based primers of the past, however, have not adhered well to lacquer topcoats which are popular as automotive finishes.
With the current emphasis on reduction of solvent emissions, the use of powder-coating compositions, including primers, which contain no solvent, has gained in popularity. Many powder coatings, however, require unacceptable high temperatures, and therefore high energy consumption, to cure. Many of those powder formulations that can be cured at lower temperatures produce a coating that can lose adhesion. Therefore, there remains a need for a powder coating composition that not only cures rapidly at commercially-acceptable temperatures but also exhibits good adhesion to lacquer topcoats and resistance to corrosion and chipping.